"It is difficult to give an exact number... probably about 100. This is my own estimate," he told reporters on Wednesday.

Under a controversial federal law approved by President Vladimir Putin last year, NGOs funded from abroad and engaged in political activities are required to register as 'foreign agents,' or face fines of up to 500,000 rubles ($16,000) for NGOs and up to 300,000 rubles ($10,000) for NGO directors.

Inspections of NGOs began in late March 2013 when the Justice Ministry said its goal was to check that these organizations' activities corresponded with the objectives of their charters and Russian legislation.

The Memorial Human Rights Center, ADC Memorial's partner, was requested to register as a foreign agent in April. The center said it would be appealing the decision. The center's head, Alexander Cherkasov, believes that its initiatives against politically motivated administrative and criminal prosecution were seen as political activity.

In April, prosecutors in Russia's republic of Tatarstan ordered the Agora human rights group, which has provided legal assistance to people detained at anti-Kremlin protests, to register as a foreign agent, a demand it has called unlawful. Agora spokesman Dmitry Kolbasin confirmed that the organization received funding from abroad, but said the nature of its activities did not require it to register as a foreign agent.

On April 25, independent election watchdog GOLOS Association, which was founded in 2000 to protect the rights of Russian voters and to foster the development of civil society, was fined 300,000 rubles ($9,500) for violating the foreign agent law. In addition, the organization's executive director Liliya Shibanova was fined 100,000 rubles ($3,200).

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